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我是 Java 新手，我创建了某种迷你游戏，我希望玩家选择是否要再次玩，我尝试将我的 start 布尔变量更改为静态类型并添加一些代码行，但是代码似乎不起作用，每次我玩游戏时，它都会问我是否要重玩，但问题是即使我最后在控制台输入“是”，游戏也没有'似乎没有重新启动。谁能帮帮我，我将不胜感激，谢谢！

import java.util.Random;
import java.util.Scanner;

//Rocks, papers, scissors game complied by William To.
public class RockPaperScissor {
static int gamePlays = 0;
static boolean start = true;
public static void main(String[] args) {
    while (start){
        @SuppressWarnings("resource")
        Scanner userInput = new Scanner(System.in);
        Random comOutput = new Random();
        System.out.println("Do you choose rock, paper or scissor?");
        String userChoice = userInput.nextLine();
        int comChoice = comOutput.nextInt(2);
        switch (userChoice){

        case "rock":
            if(comChoice == 0){
                System.out.println("I choose rock too! That's a draw!");
            } else if(comChoice == 1){
                System.out.println("I choose paper! I win!");
            } else {
                System.out.println("I choose scissor! You win!");
            }
            break;

        case "paper":
            if(comChoice == 0){
                System.out.println("I choose rock! You win!");
            } else if(comChoice == 1){
                System.out.println("I choose paper too! That's a draw!");
            } else {
                System.out.println("I choose scissor! I win!");
            }
            break;

        case "scissor":
            if(comChoice == 0){
                System.out.println("I choose rock! I win!");
            } else if(comChoice == 1){
                System.out.println("I choose paper! You win!");
            } else {
                System.out.println("I choose scissor too! That's a draw!");
            }
            break;
        default :
            System.out.println("I don't think that's an option.");
            break;
        }
        gamePlays++;
        System.out.println("You've played " + gamePlays + " games.");

               //BELOW IS THE PART I want to ask, what's wrong? 

        System.out.println("Do you want to play again?"); 
        String playAgain = userInput.next();
        if (playAgain == "yes"){
            System.out.println("Restarting game...");
            start = true;
        } else if (playAgain == "no") {
            System.out.println("Quitting game.");
            start = false;
        }
    }
}   
}

Eclipse 的打印输出：

Do you choose rock, paper or scissor?  
rock **//my input**    
I choose paper! I win!  
You've played 1 games.  
Do you want to play again?    
yes **//my input**    
Do you choose rock, paper or scissor?  
paper **//my input**    
I choose paper too! That's a draw!  
You've played 2 games.  
Do you want to play again?  
no **//my input**  
Do you choose rock, paper or scissor?
4

5 回答 5

5

Comparison between strings needs the String#equals instead of ==. So this:

if (playAgain == "yes"){
    System.out.println("Restarting game...");
    start = true;
} else if (playAgain == "no") {
    System.out.println("Quitting game.");
    start = false;
}

Has to become this:

if (playAgain.equals("yes")){
    System.out.println("Restarting game...");
    start = true;
} else if (playAgain.equals("no")) {
    System.out.println("Quitting game.");
    start = false;
}

In order to work properly.

However, I suggest to use String#equalsIgnoreCase, because with equals, the comparison is case-sensitive, so if user inputs i.e. Yes or yEs, playAgain.equals("yes") will return false

UPDATE

As Maroun Maroun says, it is better to use 

"yes".equals(playAgain)

and

"no".equals(playAgain)

Because if playAgain is null it won't throw a NullPointerException

于 2013-06-22T09:44:04.037 回答
4

尝试：

    if ("yes".equals(playAgain)) {
        System.out.println("Restarting game...");
        start = true;
    } else if ("no".equals(playAgain)) {
        System.out.println("Quitting game.");
        start = false;
    }

String#equals()检查字符串的字符相等性，==检查内存引用。

于 2013-06-22T09:46:40.233 回答
3

The problem is probably this line

if (playAgain == "yes")

(and the one later for no).

Strings in Java are objects. This means that two strings might have the same content, i.e. contain the same text, but still not be "the same" as far as == is concerned. To compare two strings and see if they contain the same text, use this:

if (playAgain.equals("yes"))
于 2013-06-22T09:44:45.087 回答
1

问题在于进行String比较的方式。

playAgain == "yes", 此检查将检查对象是否相等。

但是在这种情况下，需要比较对象的值，下面的代码将为您工作。

playAgain.equals("yes")
于 2013-06-22T15:20:48.683 回答
0

String.equals()您需要使用方法而不是比较字符串==

该equals方法比较字符串的值并==检查两个对象是否引用同一个对象。

于 2013-06-22T09:45:08.787 回答